Our broad objectives are: to ascertain the role of innate immunity in protecting against HIV-infection and disease progression; to explore the antiviral properties of primate theta-defensins and determine their mechanism of activity, and identify promising 0-defensin peptides for future therapeutic development. Theta-defensins are circular octadecapeptides. They are formed in vivo by the post-translational splicing of two nonapeptides, each derived from a truncated, alpha-defensin-like propeptide that is encoded by a DEFT gene. Some 7.5 to 10 million years ago, the DEFT genes of a hominid ancestor of Homo sapiens acquired a premature stop codon in Exon 2, which encodes the signal sequence. Consequently, although human cells still express theta-defensin mRNA, they no longer produce theta-defensin peptides. We synthesized three theta-defensin peptides (retrocyclins- 1, -2 and-3) that human ceils could have produced if their DEFT genes had not been silenced. Retrocyclin-2 was remarkably effective in protecting CD4-positive cells from infection by both T and Mtropic strains of HIV-1. Its wide protective spectrum encompassed the clade B isolates that cause most infections in our country and the Clade C isolates that predominate in southern Africa and India. Our preliminary data revealed that retrocyelins are lectins, and that they bind gp 120, CD4 and galactosylceramide with high affinity. The specific aims of this proposal are: a). To synthesize novel theta-defensins, including peptides based on DEFT gene sequences in non-human primates, b). To test theta-defensins and selected alpha- defensins (including human HN 1-3), against laboratory-adapted and wild-type strains of HIV-1, HIV-2, and SIV; c) To identify the sugars and oligosaccharides recognized by primate theta- and alpha-defensins and correlate this with their antiretroviral properties, and d) To determine which human lymphocytes express 0-defensin mRNA, and if arninoglycosides enable human cells to produce 0-defensin peptides. Health relatedness: 0- defensins constitute a novel class of HIV-uptake inhibitors with excellent potential for future therapeutic development. The proposed research will allow experienced investigators based at UCLA, The Yerkes Primate Center at Emory University and the CDC to build the required foundation for this development.